近十年洪泽湖富营养化状态变化趋势及原因分析

Ten-year Trend Analysis of Eutrophication Status and the Related Causes in Lake Hongze

通过2011~2020年洪泽湖全湖逐月监测数据的分析,厘清了近十年洪泽湖富营养化状态变化趋势、时空变化特征和驱动要素,为洪泽湖富营养化控制提供针对性建议.作为洪泽湖最主要的入湖河流,淮河近十年来高锰酸盐指数显著上升、TN显著下降.洪泽湖近十年水体总体透明度、TP浓度和高锰酸盐指数平均值显著上升,TN和Chl-a浓度的平均值显著下降,富营养化状态指数(TLI)有下降趋势.洪泽湖富营养化状态的变化趋势在空间上存在差异:洪泽湖东区是淮河的过水通道,由于较短的水体停留时间,即使在营养盐浓度较高的情况下,藻类生物量仍显著低于其他区域,同时由于淮河水质的改善,TLI显著下降;北区具有较高的水生植被覆盖度,不仅降低了水体营养盐浓度,并为浮游动物和鱼类提供了栖息地,有效地抑制了藻类的生长,富营养状态要明显低于其余湖区,近十年TLI呈现下降趋势;西区富营养化程度最高,由于内源释放的加剧,藻类生物量最高,富营养化程度并没有得到改善.洪泽湖富营养化状态也存在显著的季节差异,夏季富营养化指数最高,藻类生物量因温度升高而相对较高,同时夏季藻类生物量主要受营养盐浓度影响,其中NO_(3)^(-)-N的影响最大.针对洪泽湖富营养化状态的分布特征和成因,对不同季节和湖区应当采取相应的富营养化控制措施.

In order to propose pertinent suggestions regarding eutrophication control for Lake Hongze,we used monthly monitoring data from 2011 to 2020 to elucidate the spatiotemporal changing characteristics of eutrophic status and the relevant driving factors.As the main river entering Lake Hongze,River Huaihe experienced an increase in permanganate index and a decrease in TN in the last 10 years.Meanwhile,Secchi depth,TP,and permanganate index increased,whereas TN and Chl-a concentration decreased significantly in Lake Hongze.As a result,the eutrophic status TLI index of Lake Hongze declined over the past 10 years.The change trend of TLI in Lake Hongze differed spatially.As the main water passage of River Huaihe,the algal biomass was lower in the eastern region than that in the other two lake regions,regardless of the relatively high nutrient concentration,due to the short water retention time.Furthermore,the water quality of River Huaihe improved;thus,the TLI index decreased significantly in the eastern lake region.The northern region had a high coverage of aquatic vegetation,which not only reduced the concentration of water nutrients but also provided a habitat for zooplankton and fish,effectively inhibiting algal growth.Thus,the TLI index was lowest among the three lake areas and showed a downward trend over the last 10 years.In the western region,the algal biomass was the highest due to the intensification of phosphorus release from sediment in summer.Thus,the TLI index was the highest and had not improved in the past 10 years.There were also significant seasonal differences in the TLI of Lake Hongze,which was highest in summer,due to the relatively high algal biomass.Moreover,the algal biomass in summer was mainly affected by the concentration of nitrate.According to the spatiotemporal distribution characteristics of eutrophic status and the impacting factors in Lake Hongze,corresponding measures for eutrophication control should be taken for different seasons and lake areas.